"Three months after his father’s death, Dave was now running the shop." The next sentence will be in the present tense, because "now" tells you that "3 months after" is the current time for this topic.

"Three months after his father’s death, Dave was running the shop." The next sentence will continue a narrative of past events.

Couldn't the following sentence be the same with or without the added "now"?

Janet

<"Three months after his father’s death, Dave was now running the shop.">

Do you see the point-of-view being the reader's present there? Or, does the inclusion of "now" clearly mark the sentence as set in the present of the story. I mean, by using "now", isn't the writer attempting to shift the reader into the character/s present?

Instead of looking at the action as "then" (i.e. from the reader's present), we look at it from within (i.e. from the Now of the story).

Rather than just make it more explicit, I think that the "now" gives the importance of the second part of the sentence a sort of implied emphasis. To elaborate, it's as though it's saying "at last," or it's remarking that it's a sad chain of events.

Even more emphasis could be lent by saying "only now" (as though he'd be waiting to run the shop for some time). Unless there is supposed to be an evoked sympathy for the brief time period, in which case place "Only" before "three months." The possibilities are abundant, sorry I'm getting carried away. :)